1. Field of the Invention
The present invention relates to a router device for setting up a cut-through path and a method for controlling a cut-through path.
2. Description of the Background Art
A router device for transferring data gram by analyzing an IP (Internet Protocol) header uses a routing protocol for the purpose of determining a next hop transfer target. In one such routing protocol called OSPF (Open Shortest Path Fast) (see J. Moy, “OSPF Version 2”, Internet RFC2328, April 1998, for example), when a plurality of next hop transfer targets exist corresponding to a plurality of routes of the same cost up to a final destination network or host, it is possible to maintain a plurality of next hop transfer target information. Here, the cost refers to an information such as the number of intermediate routers to be passed, for example, where the lowest cost implies the shortest route.
This function is utilized for the load balancing in such a way that, when a router device for transferring datagrams has a plurality of next hop transfer target router information, datagrams are outputted uniformly over these next hop transfer target routers so as to avoid loading only a particular router device heavily. Here, the important point is that, at a time of the load balancing, there is a need to make sure that the orders among datagrams are not reversed in the data transfer between two hosts.
On the other hand, in the label switching technique that has been proposed as a scheme for realizing a fast transfer of datagrams such as those of IP, the IP header information is not looked during the datagram transfer so that it is difficult to guarantee the orders among datagrams in the data transfer between two hosts.
For this reason, the label switching technique adopts a scheme for setting up a plurality of paths (called label switched paths) for carrying out a cut-through transfer from a device (called edge router) that currently carries out a transfer based on the IP header, and transferring datagram to one of the plurality of cut-through paths that are set up at the edge router.
For the label switched path set up in this scheme, there exists a set up called Explicit Route which enforces passing of each path at a time of starting the set up from the edge router.
In the case of the set up according to Explicit Route, it is necessary for the edge router to recognize a deletion of a specified route (router device) due to the change of a route at an intermediate router device or the like, and at a time of notifying the deletion of the specified route from a router that detected it to the edge router, there are cases which require special means such as the use of information on the routing protocol or a protocol for generating the cut-through.
Also, in the conventional method, even when a given router itself does not have a plurality of routes, there is a need to recognize a plurality of routes, which is difficult depending on the routing protocol, so that there is a possibility for a network manager to be required to make a registration at a time of network designing.
As described, conventionally, there has been a problem that, in the case of carrying out the load balancing regarding the cut-through path, the edge router of that cut-through path that is to be route changed for the purpose of load balancing must be involved in this process. Also, for this reason, there has been a problem that the control and implementation become complicated and it is difficult to realize the effective load balancing.